Ziegler-Natta Catalyzed Polyisoprene Articles

ABSTRACT

A polymeric article comprises an elastomeric layer comprising cured synthetic polyisoprene particles that comprise a Ziegler-Natta catalyzed polyisoprene.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityof pending U.S. patent pplication Ser. No. 16/848,181, filed on Apr. 14,2020, which is a continuation of and claims the benefit of priority ofpending U.S. patent application Ser. No. 16/115,750, filed on Aug. 29,2018, now U.S. Pat. No. 10,662,269, which claims priority under 35U.S.C. § 119(e) to U.S. Provisional Application No. 62/552,859, filedAug. 31, 2017, the disclosures of which are incorporated herein byreference in their entireties.

FIELD

The present disclosure is directed to personal protective articles and,more specifically, to condoms comprising polyisoprene catalyzed byZiegler-Natta catalysts.

BACKGROUND

Prophylactic devices, such as condoms, finger cots, and gloves, such asexamination and surgical gloves, are typically made of polymericmaterials to provide protection against chemicals, abrasions, germs,viruses, and microbes among many uses. Polymeric materials includenatural rubber latex (natural polyisoprene), synthetic polyisoprene, orvarious polyurethanes. Prophylactic devices made of natural rubber arestrong. Natural rubber, sourced from Hevea Brasiliensis and/or guayule,has a high level of stereo-regularity, meaning that the polymermolecules of which it is comprised consist almost exclusively of cis-1,4isoprene units. Natural rubber latex is also a highly branched polymerwith a high molecular weight and a wide molecular weight distribution.These characteristics of the natural rubber result in vulcanized rubberproducts having a unique combination of strength and elasticity.However, natural rubber also contains proteins that produce dermalallergic reactions in some susceptible individuals.

Synthetic polyisoprene resins have been developed to provide thebenefits of natural rubber and to eliminate the potential for proteinallergy. However, some synthetic polyisoprenes, such as that produced byKraton Inc., by anionic addition polymerization, typically consist oflower levels of stereo-regularity (i.e., less than 90% cis 1,4 isoprene)and reduced molecular weight. Consequently, articles produced from suchsynthetic polyisoprenes have inferior properties compared with naturalrubber articles. In addition, synthetic polyisoprene latex with lowerlevels of stereo-regularity unfavorably flocks and agglomerates insuspension, which results in defects in dipped articles. A latex diptank of such a synthetic polyisoprene correspondingly has a limitedavailable processing window for dipping articles. Furthermore, additionof anti-flocculants interferes with cross-linking, resulting inanisotropic cure properties, e.g., poor strength and elongationproperties, such as voids and cracks due to the formation of fracturesin inter-particle and intra-particle regions.

There is an ongoing need to produce prophylactic devices, such ascondoms, finger cots, and polymeric gloves that are thin, strong andnon-allergenic.

SUMMARY

Embodiments according to the present disclosure include polymericarticles, and methods for manufacturing polymeric articles, thatcomprise synthetic polyisoprene materials catalyzed using Ziegler-Nattacatalysts, substantially as shown in and/or described in connection withat least one of the figures, as set forth more completely in the claims,are disclosed. Various advantages, aspects, and novel features of thepresent disclosure will be more fully understood from the followingdescription and drawings.

The foregoing summary is not intended, and should not be contemplated,to describe each embodiment or every implementation of the presentdisclosure. Other and further embodiments are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this disclosure and are therefore not to beconsidered limiting of its scope, for the disclosure may admit to otherequally effective embodiments. It is to be understood that elements andfeatures of one embodiment may be in other embodiments without furtherrecitation. It is further understood that, where possible, identicalreference numerals have been used to indicate comparable elements thatare common to the figures.

FIG. 1 depicts a first transmission electron microscopy (TEM) image,according to embodiments of the disclosure;

FIG. 2 depicts a second TEM image, according to embodiments of thedisclosure;

FIG. 3 depicts a third TEM image, according to embodiments of thedisclosure;

FIG. 4 depicts a fourth TEM image, according to embodiments of thedisclosure; and

FIG. 5 is a perspective schematic view of a condom according to anembodiment.

DETAILED DESCRIPTION

Embodiments described in this disclosure, briefly summarized above anddiscussed in greater detail below, comprise polymeric articles, such ascondoms, including thin-walled condoms and gloves. Embodiments maycomprise condoms or gloves that are formed using coagulants. Embodimentsmay comprise condoms and gloves that are formed using Ziegler-Nattacatalyzed synthetic polyisoprene materials. Embodiments may comprisecondoms and gloves that are made using Ziegler-Natta catalyzed syntheticpolyisoprene materials and coagulants.

The inventors have unexpectedly observed that condoms made from theZiegler-Natta catalyzed polyisoprene resins described herein haveenhanced tensile strength, allowing thinner condoms to be manufactured.Thinner condoms allow greater sensitivity to wearers. Thinner gloves aremore flexible yet unexpectedly retain puncture resistance and abrasionresistance. Any, all or some of the embodiments according to thedisclosure comprise condoms and/or polymeric gloves having a thicknessof, for example, 0.030-0.065 mm in cross-sectional thickness. Exemplaryembodiments according to the disclosure comprise condoms or polymericgloves that are 0.040-0.055 mm in cross-sectional thickness.

Embodiments of the disclosure further comprise gloves, such asexamination gloves, surgical gloves, and gloves for household use, andfinger cots. Embodiments further comprise gloves that are formed usingcoagulants. Embodiments comprise a polymeric glove that includes a thumbhaving a front surface and a back surface; a plurality of fingers, apalm region; and a backhand region.

Embodiments of the disclosure further comprise condoms. Embodimentsfurther comprise condoms that are formed using coagulants. Embodimentscomprise a condom that includes an open end, a closed end, and a tubularsheath extending from the closed end to the open end. FIG. 5 is aperspective schematic view of a condom according to an embodiment. TheZN catalyzed PI condom 100 disclosed herein comprises a closed end 104and an open end 108. A tubular shaft 106 extends from the closed end 104to the open end 108, which has an opening 110 opposite a teat end 102 ofthe closed end 104. Optionally, the condom further comprises a bead 114.The tubular shaft of the condom comprises the ZN catalyzed PI particles,which may be provided by an aqueous ZN catalyzed PI latex composition.The aqueous latex compositions may have a solids content in the range of60% to 65% by weight. The compositions may further comprise additionalwater, preferably deionized water, to result in a composition solidscontent in the range of 55% to 60% by weight. Optionally, the aqueouslatex compositions may further comprise one or more thickeners and/orstablizers/surfactants. Colorants and/or pigments may optionally beadded to the aqueous latex compositions.

Before describing embodiments of the present disclosure in detail, theterminology used herein is for the purpose of describing particularembodiments only, and is not intended to be limiting. The embodimentsdescribed herein should not necessarily be limited to specificcompositions, materials, designs or equipment, as such may vary. Alltechnical and scientific terms used herein have the usual meaningconventionally understood by persons skilled in the art to which thisdisclosure pertains, unless context defines otherwise. Also, as used inthis specification and the appended claims, the singular forms “a,”“an,” and “the” include plural referents unless the context clearlydictates otherwise.

The term “flexing” or “flex” refers to finger movements, such as bendingfingers, making a fist, gripping, grasping, clenching or otherwisefolding the fingers.

The terms “emulsion,” “dispersion,” “latex” and “suspension” aregenerally analogous and indicate a system in which small particles of asubstance, such as rubber particles, are mixed with a fluid solvent(such as water and/or alcohols and/or other organic fluids) but are atleast partially undissolved and kept dispersed by agitation (mechanicalsuspension) and/or by the molecular forces in a surrounding medium(colloidal suspension). Emulsions contemplated herein may furthercomprise typical and suitable components for rubber or elastomericformulations and compounds, such as accelerators, such as guanidines,thiazoles, thiurams, sulfenamides, thioureas, dithiocarbamates, andxanthanates. Emulsions contemplated herein may further compriseactivators, such as zinc oxides, cross-linking agents and curatives,such as elemental sulfur, mono-sulphidic donors, di-sulphidic donors,such as tetramethyl thiuram disulphide and tetraethyl thiuramdisulphide; and/or polysulphidic donors, such as xanthogen polysulphideand dipentamethylene thiuramtetrasulfide. Emulsions contemplated hereinmay further comprise anti-oxidants and/or anti-ozonants. At least onesuitable anti-oxidant is Wingstay L. Emulsions contemplated herein mayfurther comprise, surfactants, such as sodium dodecyl sulfates andpolyvinyl alcohols. Emulsions contemplated herein may further compriserheology-modifiers, such as various clays and aluminosilicates, pHadjusters, such as hydroxides, such as potassium hydroxide, pigments,processing agents, and/or fillers as are known to those in the art.

The term “polymer” generally includes, but is not limited to,homopolymers, copolymers, such as for example, block, graft, random andalternating copolymers, terpolymers, etc. Furthermore, unless otherwisespecifically limited, the term “polymer” includes all possiblegeometrical configurations of the molecule. These configurationsinclude, but are not limited to isotactic, syndiotactic and randomsymmetries.

The term “thermoplastic” generally includes polymer materials thatbecome reversibly pliable, moldable, and heatable above a specifictemperature and solidify upon cooling. The term “thermoset” generallyincludes polymer materials that strengthen following heating andsolidification, and cannot be reheated and re-formed after an initialforming. The term “thermoplastic elastomer” (TPE) denotes a class ofcopolymers comprising both thermoplastic and thermoset moieties,producing materials having properties of both moieties. The term“rubber” generally indicates elastomers produced from natural rubberlatexes or synthetic elastomers.

A method for producing synthetic polyisoprene articles comprises usingemulsions of synthetic polyisoprene resins catalyzed using Ziegler-Nattacatalysts. Generally, synthetic polyisoprene particles of Ziegler-Nattacatalyzed polyisoprene material comprise 96% cis-1,4-polyisoprene ormore. The synthetic polyisoprene particles may comprise a medianparticle diameter in the range of approximately from 0.2 to 2micrometers. Preferably from 0.2 to 1.5 micrometers. Exemplary syntheticpolyisoprene materials are supplied by BST Elastomer Co., Ltd, locatedin Thailand. The method may further comprise a pre-vulcanizationcomposition and post-vulcanization composition along with conventionalemulsion additives, such as stabilizers, pH control agents,antioxidants, and preservatives, etc. A typical synthetic polyisoprenelatex composition is provided in terms of 100 parts by weight of dryrubber (PHR). During compounding, the components of the latexcomposition may be suspended in aqueous and/or organic solvents.

In general, a pre-vulcanizing composition includes sulfur in the rangeof 0.6 to 1.8 PHR. An accelerator package includes zincdiethyldithiocarbamate (ZDEC) and/or zinc dibutyldithiocarbamate (ZDBC)accelerator, and/or sodium dibutyldithiocarbamate (SDBC) accelerator, adiisopropyl xanthogen polysulphide (DIXP) accelerator and/or adipentamethylene thiuramtetrasulfide (DPTT) accelerator. Thepre-vulcanizing composition may comprise a total accelerator content isin the range of 0.6 to 2.5 PHR. The pre-vulcanizing composition maycomprise a zinc oxide activator. The pre-vulcanization composition maycomprise a surfactant, i.e., a wetting agent. The surfactant may be asalt of a fatty acid, such as sodium stearate, sodium oleate, orpotassium caprylate. Some embodiments comprise more than one surfactant,e.g., potassium caprylate, also known as potassium salt of octanic acidand sodium dodecyl benzene sulphonate (SDBS). Exemplary embodimentscomprise a surfactant package having potassium caprylate, sodium dodecylbenzene sulphonate (SDBS) and polyoxyethylene cetyl/stearyl ether in therange of 0.3 to approximately 1.5 PHR. An anti-oxidant and preservativepackage includes a butylated reaction product of p-cresol and,optionally, dicyclopentadiene in the range of 0.3 to approximately 1.0PHR.

The sulfur in the pre-vulcanizing package is, for example, elementalsulfur having a high soluble sulfur content, typically of the S₈ ringstructure. The pre-vulcanization composition further comprises anaccelerator. For example, an accelerator that can break or disrupt theS₈ sulfur ring structure is zinc dithiocarbamate. Reference to “highsoluble sulfur content” means having enough soluble sulfur present toform sufficient to permeate into latex particles in the aqueous latexemulsion and crosslink during curing to achieve commercially acceptablearticles, such as condoms and/or gloves. The pre-vulcanization of thesynthetic latex particles in the latex occurs over a period of time,e.g., 9 hours to 2 days depending on the temperature of the latex, whichis generally in the range of 20° C. to 30° C. The degree ofpre-vulcanization at different points after initial compounding of thesynthetic latex particles may be monitored by at least one of fourtests. An equilibrium-swelling test, which uses any suitable solvent,measures the equilibrium swelling of films dried down from the syntheticlatex. A relaxed modulus test gauges the vulcanization of the relaxedmodulus at 100% extension (MR100) of films dried down from the dissolvedlatex. Similarly, a pre-vulcanized relaxed modulus test (PRM) measuresthe relaxed modulus at 100% extension of the pre-vulcanized films.

A Toluene Swell Index (TSI) test may be used to measure the level ofcrosslinking by immersing the dried casted film sample in the tolueneand calculate the swollen rate. TSI may be substituted with anisopropanol index test. Cast film of the compounded latex to producefilm thickness of 0.10-0.15 mm and dry the film at 50+/−3 degree Celsiusfor 10 minutes and/or leave the film at ambient temperature until it isfully dried. Peel off the film with the powder such as corn starch orCaCO₃ to prevent the film surface being stick to itself. Cut a discsample with a die cutter. Submerge the disc film into the toluene for 60minutes. Measure the diameter of the swollen film. Calculate the %swollen by subtract the original disc diameter from the swollen filmdiameter and divided by the original film diameter. The latex particlesprogress from a non-crosslink stage (index>220%), to a partial crosslinkstage (index<220%), then to a semi-crosslink stage (index<180%) andfinally to a fully crosslink stage (index<100%) as pre-vulcanizingsulfur is incorporated within the particle.

Compounding methods according to embodiments of the disclosure includedissolving a latex composition in an aqueous solvent and stirringperiodically and examining for permeation of pre-vulcanization agentsinto the synthetic polyisoprene particles for example, by using anisopropanol index test. Polyisoprene latex has an inherent tendency toflock and ‘case harden’ due to a peripheral reaction with sulfurcatalyzed by ZDBC or ZDEC, i.e., an outside surface hardens, preventingcrosslinking of internal molecules. The presence of surfactants andcreation of opened out S8 chains of sulfur enables the diffusion ofsulfur into the particles. In other words, the diffusion of sulfur intothe particles, i.e., ‘through-hardening’ can occur, allowing thecrosslinking of internal molecules. A latex article or productcomprising a through-hardened structure is stronger than an otherwisesimilar latex article or product having a case-hardened structure.

The pre-vulcanization composition provides sulfur to syntheticpolyisoprene latex particles in the aqueous synthetic polyisopreneemulsion for pre-vulcanizing the intra-particle regions. Duringpre-vulcanization, the ring structure of the sulfur is broken by thecatalytic action of the accelerator, e.g., zinc dithiocarbamate, whichpenetrates the polyisoprene particles and initially interacts with theisoprene double bonds therein.

Without intending to be bound by theory, it is believed that thepenetration of the components of the pre-vulcanizing composition intothe polyisoprene particles is a function of the diffusion process, whichmay be a linear function of time. The penetration of the componentscomprises an exponential function of temperature, reflecting a thermallyactivated process. Therefore, increasing the temperature by a fewdegrees during the pre-vulcanization step increases thepre-vulcanization rate. For example, pre-vulcanization at roomtemperature may be about 3-5 days or as much as about 9 days, whilepre-vulcanization at, for e.g., about 50-70° C., may take about 3-7hours. In the absence of pre-vulcanization of the synthetic polyisopreneparticles, crosslinking predominantly occurs in the periphery (i.e.,case-hardening) of the synthetic polyisoprene particles, resulting inweak particles. Attempts to crosslink the inter-particle region withinthe particles only during post-vulcanization, discussed below, resultsin over crosslinking of the intra-particle regions, which, in turn,results in a latex product with poor stretch properties.

The post-vulcanization composition includes amorphous or polysulfur,which is insoluble at latex emulsion temperature, e.g. 20-40° C., but issoluble at a vulcanization or cure temperature, e.g., 110-150° C.Generally, the post-vulcanization composition comprises acceleratorssuch as, but not limited to, zinc diethyldithiocarbamate (ZDEC), zincdibutyldithiocarbamate (ZDBC), sodium diethyldithiocarbamate (SDEC),sodium dibutyldithiocarbamate (SDBC), a thiuram compound and axanthogen. Examples of suitable xanthogens include, but are not limitedto, diisopropyl xanthogen polysulphide (DIXP), diisopropyl xanthogen,tetraethylthiuram disulfide, and xanthogen sulfide. DIXP is a suitablexanthogen owing to its polysulphidic donor properties. Thepost-vulcanization composition may further comprise a thiuramaccelerator. An example of a polysulphidic thiuram accelerator isdipentamethylene thiuramtetrasulfide (DPTT). Another example of athiuram compound is tetrabenzyl thiuram disulfide. Zinc oxide may alsobe added as an activator.

The post-vulcanization composition provides the ability to crosslinkregions between the particles of synthetic polyisoprene orinter-particle regions thereby assuring a high quality substantiallyuniformly cured synthetic polyisoprene product.

The post-vulcanization composition activates inter-particlecross-linking at a temperature of, e.g., 100-150° C. In addition,post-vulcanization processes also crosslink the synthetic polyisopreneparticles with sulfur. Such post-vulcanization results in a morehomogeneous latex coating having greater strength and elongationproperties. The composition produced is stable for up to approximately 5days at 20° C. to 25° C. and is useful for a production line.

Table 1 shows at least one exemplary embodiment of a Ziegler-Natta (ZN)catalyzed synthetic polyisoprene resin latex composition for producing apolymeric article. The latex composition is preferably aqueous.

TABLE 1 Formulation - ZN Catalyzed Quantity per hundred dry rubberComponent (PHR) Synthetic Polyisoprene Resin ZN 100 (e.g., see Table 2)Alkyl Aryl Sulphonate 0.1-0.3  Potassium Caprylate/Potassium Oleate0.1-0.46 Polyoxyethylene cetyl/Stearyl Ether 0.1-0.5  Sulfur 0.8-1.8Reactive Zinc Oxide 0.05-0.5  ZDEC/ZDBC 0.4-1.0 SDBC/SDEC 0.05-0.5 DIXP/Diisopropyl Xanthogen/ 0.2-0.6 Xanthogen Sulfide Anti-oxidant0.5-1.0

Table 2 below shows a comparison of pre-vulcanization behavior of anexemplary anionic polyisoprene and an exemplary Ziegler-Natta catalyzedsynthetic polyisoprene resin.

TABLE 2 PI Resins Anionic IR Ziegler-Natta (ZN) Microstructure Medianparticle size (μm) Max 1.8 Max 1.5 Cis-1,4 (% wt) 92 96-97 Trans-1,4 (%wt) 1.50 0.50 3,4-isomers (% wt) 6.50 2.5-3.5 Macrostructure LinearBranched Molecular weight distribution Narrow Narrow Avg molecularweight (*10⁶ g/mol) 2-3 1 Gel (% wt) Intrinsically nil 10.0-20.0 Ash (%wt) 0.05-0.1  0.15-3.0  Trace metal content (ppm) 70  400-3000Stabiliser content (% wt) 0.05-0.3  1 TSC (%) 63 60-64 Viscosity (cps)150  50-150 pH  9.5-12.0 10.0-12.0 Specific gravity 0.91 0.91 ColorAmber Light yellow Residual solvent (ppm) 1500 (0.15%) 1000 (0.10%)

The present disclosure further provides a method of forming a syntheticpolyisoprene polymeric article. The method comprises disposing anelastomeric coating of a Ziegler-Natta catalyzed polyisoprene materialon a former and curing the elastomeric coating to form an elastomericlayer of the polymeric article. The disposing step may comprise dippinga coagulant-free or coagulant coated former in an emulsion of theZiegler-Natta catalyzed polyisoprene material, which may be an aqueouslatex composition according to Table 1 having pre-vulcanized particles,at least once to form a thin layer of latex or elastomeric coating withindividual particles of pre-vulcanized synthetic polyisoprene on thesurface of the former. The former can be any suitable former as is knownin the art. The present inventive composition is particularly useful forlayering onto formers for condoms and gloves.

Embodiments of the Ziegler-Natta catalyzed formulations disclosed inTable 1, which may use ZN PI resins of Table 2, as well as otherZiegler-Natta catalyzed formulations, are capable of making condoms thathave a lighter color than natural rubber condoms, allowing a greaterrange of colored condoms to be manufactured, while maintaining similarhardness and tensile strength properties. Furthermore, any residualsolvent content in condoms made therefrom is lower, lending to lesserallergenicity. Further still, the allergenicity of condoms made fromZiegler-Natta catalyzed formulations is lower compared with naturalrubber and anionic formulations, owing to lesser amounts of acceleratorsand sulfur. The branched molecular structure of the Ziegler-Nattacatalyzed synthetic polyisoprene provides greater strength than linearmolecular structure of an anionic catalyst produced latex. TheZiegler-Natta catalyzed synthetic polyisoprene also comprises a greateramount of cis character, e.g., cis-1,4 isomer, of the polyisoprenemolecules than the anionic catalyzed polyisoprene, improving thestrength properties of products made with Ziegler-Natta catalyzedsynthetic polyisoprene.

Also, the exemplary Ziegler-Natta catalyzed formulation of Table 1 haspotentially lower total solids content, allowing the manufacture ofthinner condoms. And, the exemplary Ziegler-Natta catalyzed formulationof Table 1 has potentially lower viscosities during the dippingprocesses, allowing thinner condoms to be produced therefrom. Lowerviscosities also allow a faster line speed during manufacturing. In atleast some embodiments, unlike other condom manufacturing, coagulantsmay be disposed on condom formers prior to the disposition of aZiegler-Natta catalyzed polymeric coating on the formers, allowing astronger condom to be manufactured at similar thicknesses compared withanionic polymerized condom formulations.

Furthermore, the Ziegler-Natta catalyzed formulation of Table 1 producessmaller particle sizes, which allows a thinner film and improve usersensitivity during sexual intercourse and/or glove use. Smallerparticles also exhibit improved crosslinking, which improves theprocess-ability of thinner products. For example, preventing the condomor glove collapse during washing processes and allows powder to coatevenly on both inside and outside and, therefore, reducing defects.

Table 3 lists a typical dipping method for producing a condom using aZiegler-Natta catalyzed polyisoprene resin that is pre-vulcanized, asdescribed above. A similar method can be created for a syntheticpolyisoprene surgical glove.

TABLE 3 First dip (thickness of coating may be controlled by latexviscosity and/or former speed in the dip tank Drying of the latexcoating (60-80° C.; 1-3 min). Second dip (optional) Drying of the latexcoating (60-80° C.; approx 1-3 min). Beading/ring formation on the openend of the condom Drying of the ring and latex coating (70-100° C.;approx 1-3 min) Curing (110-130° C.; approx 11-15 min) Leaching (70-80°C.; approx 1-2 min) Stripping of the condoms from the formers

The method of dipping for the condoms using the surfactant-stabilized,pre-vulcanized synthetic polyisoprene latex composition is typicallywithin the 5-day period, e.g., an average lifetime of syntheticpolyisoprene latex emulsion tank. A condom former is dipped in thecomposition in a first dip. The wall thickness of the latex coating iscontrolled by the viscosity of latex, which is a function of the totalsolids content of the composition in the dip tank. The speed of movementof the formers while dipping also affects the wall thickness. The latexcoating that coats the formers is dried at approximately 60-100° C. forapproximately 1-3 minutes. The latex coating on the former is,optionally, dipped again into the composition to apply a second dipcoating. The latex coating after the second dip is dried atapproximately 60-80° C. for approximately 1-3 minutes. The open end ofthe condom is rolled to create a bead ring, which is distal to a tip ofa closed end of the condom.

The coating can be post-vulcanized by heating the coating, e.g., toabout 110 to 150° C. for approximately 8 to 15 minutes, to form anelastomeric layer of a condom. Exemplary embodiments includepost-vulcanization that is achieved by heating in an oven atapproximately 120° C. for approximately 12 minutes. During this period,the inter-particle regions are cross-linked. The intra-particle regionsalso undergo further crosslinking, producing a more homogeneous latexproduct. The condom is optionally leached in water at approximately70-80° C. for about 1-2 minutes to remove residual surfactants andcross-linking agents from the condom. The condom is then stripped fromthe former. The latex articles, such as condoms, produced display higherstrength and improved stretch, even when a low stereo-regularitysynthetic polyisoprene is used. The synthetic polyisoprene articles arefree from irritation-causing proteins that cause latex sensitivityissues.

Embodiments according to the disclosure comprise the use of a coagulantsolution to wet the former and may include an exemplary aqueous solutionof 5% calcium nitrate, although other concentrations are possible as areknown to those in the art, such as an aqueous solution ranging inconcentration from 6-40% calcium nitrate. Other salts, such as calciumchloride, calcium citrate, aluminum sulfate, and the like and/ormixtures thereof may be used. Furthermore, the coagulant solution may beaqueous, alcoholic, or a mixture of aqueous and alcoholicsolutions/solvents. Weaker acid solutions may also be used ascoagulants, such as formic acid, acetic acid, and other low pKa acids asare known to those in the art.

Embodiments according to the disclosure comprise the use ofpre-vulcanizing and post-vulcanizing methods, the technology of which isdisclosed in commonly-assigned U.S. Pat. Nos. 8,087,412; 8,464,719;9,074,027; and 9,074,029 which are incorporated by reference inentirety. Methods for determining the molecular weight betweencrosslinks M_(c) is disclosed in U.S. Pat. Nos. 8,087,412; 8,464,719;9,074,027; and 9,074,029.

EMBODIMENTS

Embodiment 1. A polymeric article comprising: an elastomeric layercomprising cured synthetic polyisoprene particles that comprise aZiegler-Natta catalyzed polyisoprene material.

Embodiment 2. The polymeric article of the preceding embodiment, whereinthe synthetic polyisoprene particles are pre-vulcanized.

Embodiment 3. The polymeric article of any preceding embodiment, whereinthe Ziegler-Natta catalyzed polyisoprene material comprises a branchedmacrostructure.

Embodiment 4. The polymeric article of any preceding embodiment, whereinthe Ziegler-Natta catalyzed polyisoprene material comprises a cis-1,4isomer content of 95% by weight or greater.

Embodiment 5. The polymeric article of any preceding embodiment, whereinthe Ziegler-Natta catalyzed polyisoprene material comprises a cis-1,4isomer content of about 96% to 97% by weight.

Embodiment 6. The polymeric article of any preceding embodiment, whereinthe Ziegler-Natta catalyzed polyisoprene material comprises a trans-1,4isomer content of 1% by weight or less.

Embodiment 7. The polymeric article of any preceding embodiment, whereinthe Ziegler-Natta catalyzed polyisoprene material comprises a 3,4 isomercontent of 5% by weight or less.

Embodiment 8. The polymeric article of any preceding embodiment, whereinthe article has a thickness in the range of from 0.030 to 0.065 mm.

Embodiment 9. The polymeric article of any preceding embodiment, whereinthe elastomeric layer comprises a post-vulcanized structure having amolecular weight between crosslinks (Mc) of less than 11,000 g/mol.

Embodiment 10. The polymeric article of any preceding embodiment,wherein the synthetic polyisoprene particles have a median particlediameter in the range of approximately from 0.2 to 2 micrometers, or thesynthetic polyisoprene particles have a median particle diameter in therange of approximately from 0.2 to 1.5 micrometers.

Embodiment 11. The polymeric article of any preceding embodiment,wherein the synthetic polyisoprene particles are bonded to each otherthrough intra-polyisoprene particle crosslinks and inter-polyisopreneparticle crosslinks.

Embodiment 12. The polymeric article of any preceding embodiment in theform of a condom.

Embodiment 13. A condom comprising: an elastomeric layer comprisingcured synthetic polyisoprene particles that are pre-vulcanized, whereinthe synthetic polyisoprene particles comprise a Ziegler-Natta catalyzedpolyisoprene material that comprises: a cis-1,4 isomer content of 95% byweight or greater; a trans-1,4 isomer content of 1% by weight or less;and a 3,4 isomer content of 5% by weight or less.

Embodiment 14. The condom of the preceding embodiment, wherein theelastomeric layer forms an open end, a closed end, and a tubular sheathextending from the closed end to the open end.

Embodiment 15. The condom of any of embodiment 13 to the precedingembodiment, wherein the Ziegler-Natta catalyzed polyisoprene materialcomprises a branched macrostructure.

Embodiment 16. The condom of any of embodiment 13 to the precedingembodiment, wherein the elastomeric layer comprises a post-vulcanizedstructure having a molecular weight between crosslinks (Mc) of less than11,000 g/mol.

Embodiment 17. The condom of any of embodiment 13 to the precedingembodiment, wherein the synthetic polyisoprene particles have a medianparticle diameter in the range of approximately from 0.2 to 1.5micrometers.

Embodiment 18. The polymeric article of any of embodiment 13 to thepreceding embodiment, wherein the synthetic polyisoprene particles arebonded to each other through intra-polyisoprene particle crosslinks andinter-polyisoprene particle crosslinks.

Embodiment 19. A method for producing a polymeric article, comprising:disposing an elastomeric coating of a Ziegler-Natta catalyzedpolyisoprene material on a former; and curing the elastomeric coating toform an elastomeric layer of the polymeric article.

Embodiment 20. The method of the preceding embodiment, wherein thedisposing of the elastomeric coating on the former comprises dipping theformer into an emulsion of the Ziegler-Natta catalyzed polyisoprenematerial.

Embodiment 21. The method of any of embodiment 19 to the precedingembodiment, wherein the emulsion of the Ziegler-Natta catalyzedpolyisoprene material is pre-vulcanized before dipping the former.

Embodiment 22. The method of any of embodiment 19 to the precedingembodiment, wherein the polymeric article comprises a condom and theelastomeric layer forms an open end, a closed end, and a tubular sheathextending from the closed end to the open end.

Embodiment 23. The method of any of embodiment 19 to the precedingembodiment, wherein the synthetic polyisoprene particles are bonded toeach other through intra-polyisoprene particle crosslinks andinter-polyisoprene particle crosslinks.

EXAMPLES

Condoms according to a formulation of Table 1 were produced.

A method of measuring molecular weight distribution and calculatingcrosslink density requires cutting of disks from condom samples andswelling the disk samples in toluene until equilibrium. The disks wereinitially weighed and after swelling they are weighed again. Theequilibrium volume fraction of the swelled rubber was calculated usingequation shown below. In this equation Pris the density of rubber (0.92g/cm³), P_(s) is the density of toluene (0.862 g/cm³), W_(r) is theweight of rubber before swelling and Ws is the weight of swelled rubber.

WrPrWrPr+Ws−WrPs

The volume fraction was used in the Florey-Rehner equation shown belowto calculate the crosslink density. In this equation n is the crosslinkdensity, V_(s) is the molar volume of toluene the swelling solvent whichis 106.3 cm3/mol, V_(r) is the volume fraction of the rubber phase inthe swollen gel, and X is the toluene-cis polyisoprene interactionparameter, which is 0.39.

n=−1/V _(s) multiplied by [In (1−Vr)+Vr+X Vr2][Vr13−0.5 Vr]

The molecular weight between crosslinks was calculated by the followingequation. Mc=Prn

Example 1

Table 4 shown below reports measured molecular weight between crosslinksand corresponding crosslink density for several of syntheticpolyisoprene condoms manufactured according the embodiments of thesubject disclosure. The higher the molecular weight between crosslinks,the lower the crosslink density becomes.

The data presented indicates that the process of the present disclosureresults in synthetic polyisoprene condoms that have very consistentmolecular weight between crosslinks, providing a condom having adequatemechanical properties. The molecular weight between crosslinks (Me) forthe condoms according to the present embodiments is 0.0000845 mol/cm³,which is comparable to that of natural rubber, which has a crosslinkdensity of 0.0000159 mol/cm³.

TABLE 4 Molecular Weight Original Average weight, Swollen Average McSample mg weight, mg Vr Vr N g/mol 1 76.1 460.8 0.1564 0.1564 8.452 ×10⁻⁵ 10886 2 76.3 448.1 0.1613 3 74.9 467.6 0.1516

FIG. 1 depicts a first transmission electron microscopy (TEM) image of asurface of a condom, according to embodiments of the disclosure.

FIG. 2 depicts a second TEM image of a surface of a condom, according toembodiments of the disclosure;

FIG. 3 depicts a third TEM image of a surface of a condom, according toembodiments of the disclosure; and

FIG. 4 depicts a fourth TEM image of a surface of a condom, according toembodiments of the disclosure.

The condoms studied in the first, second, third, and fourth TEM imageswere prepared as follows. Each condom was washed in propan-2-ol toremove the lubricant and then dipped in propan-2-ol containing a smallamount of talc to prevent adhesion and thus also facilitate handling.The condom was then air-dried. A number of rings were cut from thecondom using a parallel, twin-blade cutter with the blades a nominal 10mm apart. These rings were to be used for the two methods of analysis:network visualization by TEM and Vr measurement by equilibrium swelling.

Network visualization. After extraction overnight in acetone, the sampleof condom was swelled to equilibrium in styrene. The sample was thentransferred to gelatin capsules and polymerized by heating. Ultra-thinsections were then prepared by ultramicrotomy at room temperature usingglass knives. The sections were collected on a water-filled though andrelaxed with xylene vapor before collecting on TEM grids. The sectionswere then stained with osmium tetroxide vapor for one hour. Osmiumtetroxide reacts with carbon-carton double bonds and therefore shows upthe rubber network as darker than the polystyrene. Representative TEMmicrographs are provided (see TEM16803-6) in FIGS. 1-4.

The latex particles were fairly closely bonded together but theboundaries between the particles could often be seen. The samples alsocontain many voids, i.e. areas where the styrene has infiltrated to forma large pale area. Some of these voids contain small dark particles soit seems likely that most or all of them are caused by styrene formingpools around these particles which have not bonded to the rubber. A voidwhich appears to be empty may actually contain a particle which is notvisible because it was either above or below the section.

There are also some small dark patches inside some of the rubberparticles. These do not look like particles but seem to be small areasof the rubber network which have some electron-dense (i.e. high atomicnumber) material attached to them.

The uncertainty on the scalebar dimension is ±10% in all of the TEMmicrographs.

The latex particles, i.e., synthetic polyisoprene particles catalyzedusing Ziegler-Natta catalysts, exhibited close bonding.

All numerical values recited herein are exemplary, are not to beconsidered limiting, and include ranges therebetween, and can beinclusive or exclusive of the endpoints. Optional included ranges can befrom integer values therebetween, at the order of magnitude recited orthe next smaller order of magnitude. For example, if the lower rangevalue is 0.1, optional included endpoints can be 0.2, 0.3, 0.4 . . .1.1, 1.2, and the like, as well as 1, 2, 3 and the like; if the higherrange is 10, optional included endpoints can be 7, 6, and the like, aswell as 7.9, 7.8, and the like.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate comparable elements that are commonto the figures. The figures are not drawn to scale and may be simplifiedfor clarity. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

It is to be understood that various changes and modifications to theembodiments described herein will be apparent to those skilled in theart. Such changes and modifications can be made without departing fromthe spirit and scope of the present disclosure and without demising theattendant advantages. It is, therefore, intended that such changes andmodifications be covered by the appended claims.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

1. A polymeric article comprising: an elastomeric layer comprising curedsynthetic polyisoprene particles that comprise a Ziegler-Natta catalyzedpolyisoprene material comprising: a cis-1,4 isomer content of greaterthan or equal to 95% by weight to less than or equal to 97% by weight; atrans-1,4 isomer content of 1% by weight or less; and a 3,4 isomercontent of 5% by weight or less.
 2. The polymeric article of claim 1,wherein the synthetic polyisoprene particles are pre-vulcanized.
 3. Thepolymeric article of claim 1, wherein the Ziegler-Natta catalyzedpolyisoprene material comprises a cis-1,4 isomer content of about 96% to97% by weight.
 4. The polymeric article of claim 1, wherein the articlehas a thickness in the range of from 0.030 to 0.065 mm.
 5. The polymericarticle of claim 1, wherein the elastomeric layer comprises apost-vulcanized structure having a molecular weight between crosslinks(M_(c)) of less than 11,000 g/mol.
 6. The polymeric article of claim 1,wherein the synthetic polyisoprene particles have a median particlediameter in the range of approximately from 0.2 to 2 micrometers.
 7. Thepolymeric article of claim 1, wherein the synthetic polyisopreneparticles are bonded to each other through intra-polyisoprene particlecrosslinks and inter-polyisoprene particle crosslinks.
 8. The polymericarticle of claim 7, wherein the intra-polyisoprene particle crosslinksand inter-polyisoprene particle crosslinks comprise sulfur-crosslinks.9. The polymeric article of claim 1 in the form of a condom, a fingercot, or a glove.
 10. A prophylactic device comprising: an elastomericlayer comprising cured synthetic polyisoprene particles that arepre-vulcanized, wherein the synthetic polyisoprene particles comprise aZiegler-Natta catalyzed polyisoprene material that comprises: a cis-1,4isomer content of greater than or equal to 95% by weight to less than orequal to 97% by weight; a trans-1,4 isomer content of 1% by weight orless; and a 3,4 isomer content of 5% by weight or less.
 11. Theprophylactic device of claim 10 in the form of a condom, wherein theelastomeric layer forms an open end, a closed end, and a tubular sheathextending from the closed end to the open end.
 12. The prophylacticdevice of claim 10, wherein the elastomeric layer comprises apost-vulcanized structure having a molecular weight between crosslinks(M_(c)) of less than 11,000 g/mol.
 13. The prophylactic device of claim10, wherein the synthetic polyisoprene particles have a median particlediameter in the range of approximately from 0.2 to 1.5 micrometers. 14.The prophylactic device of claim 10, wherein the elastomeric layerfurther comprises intra-polyisoprene particle sulfur-crosslinks, andinter-polyisoprene particle sulfur-crosslinks.
 15. A method forproducing a polymeric article, comprising: disposing an elastomericcoating of a Ziegler-Natta catalyzed polyisoprene material comprising: acis-1,4 isomer content of greater than or equal to 95% by weight to lessthan or equal to 97% by weight; a trans-1,4 isomer content of 1% byweight or less; and a 3,4 isomer content of 5% by weight or less on aformer; and curing the elastomeric coating to form an elastomeric layerof the polymeric article.
 16. The method of claim 15, wherein thedisposing of the elastomeric coating on the former comprises dipping theformer into an emulsion of the Ziegler-Natta catalyzed polyisoprenematerial.
 17. The method of claim 15, wherein the Ziegler-Nattacatalyzed polyisoprene material is pre-vulcanized in the presence of apre-vulcanization composition before dipping the former, wherein thepre-vulcanization composition comprises: soluble sulfur, adithiocarbamate accelerator, and a surfactant.
 18. The method of claim15, wherein the polymeric article comprises a prophylactic device. 19.The method of claim 15, wherein the elastomeric layer comprises apost-vulcanized structure having a molecular weight between crosslinks(M_(c)) of less than 11,000 g/mol.
 20. The method of claim 17, furthercomprising adding a post-vulcanization composition to the emulsion afterthe Ziegler-Natta catalyzed polyisoprene material is pre-vulcanized,wherein the post-vulcanization composition comprises amorphous sulfur orpolysulfur and an accelerator.